Field of the Invention
The present invention relates to image processing of performing high dynamic range (HDR) composition of panoramic images.
Description of the Related Art
Panoramic shooting of shooting a plurality of images and composing the shot images into one image by joining them has widely been performed. Since a panoramic image has a very wide angle of view, sunlight or light of a street lamp is captured in outdoor shooting, and a region from a dark place at the deep end of a room to a bright place outside a window is captured in indoor shooting, resulting in an image having a very wide dynamic range in which the difference between a bright region and a dark region is large. Thus, if shooting is performed with a single exposure, “blown out highlights” may occur in a bright region and “blocked up shadows” may occur in a dark region.
The “blown out highlights” indicate that the color distribution of a shot image is localized on the white side due to overexposure, and some pixels are filled with white (pixels values are saturated). The “blocked up shadows” indicate that the color distribution of a shot image is localized on the black side due to underexposure, and some pixels are filled with black (pixel values are saturated). To acquire a panoramic image, there is proposed a method of acquiring a panoramic image without any blown out highlights or blocked up shadows by composing a plurality of low dynamic range images, which have been shot while changing the exposure, using an HDR composition method. Japanese Patent Laid-Open No. 2013-175827 proposes a method of performing HDR composition of panoramically composed images.
In the method proposed by Japanese Patent Laid-Open No. 2013-175827, however, it is necessary to perform shooting while changing the exposure for all the angles of view of a shooting target object, thereby complicating a procedure at the time of shooting. Furthermore, when composing adjacent shot images or images shot with different exposures, if the images include blown out highlights or blocked up shadows, no appropriate composition processing is performed, thereby obtaining an unnatural composition result in which misalignment occurs at the joint between the images.